Google, which first acknowledged the outage at 11:12 am Pacific Time, said a little over an hour later that the problem with Gmail had been resolved.

As of late Friday, the company did not offer an explanation for the outage, which affected users in at least India, Britain and United States and prompted a stream of complaints on Twitter from users in many more countries.

"We're investigating reports of an issue with Gmail. We will provide more information shortly," the company said on its "App Status" dashboard online, which tracks the state of various Google services.

Google Docs, the cloud-based productivity application that competes against Microsoft Corp's Office suite, also suffered a service disruption, according to the Google dashboard. Other Google properties, the social network Google Plus, and YouTube, appeared to load slowly as well.

Google apologizes after online services stumble

Google apologized after the Internet giant's widely used free email and an array of other services were disrupted by apparent software woes.

"Earlier today, most Google users who use logged-in services like Gmail, Google+, Calendar and Documents found they were unable to access those services for approximately 25 minutes," Google engineering vice president Ben Treynor said in a blog post.

"For about 10 percent of users, the problem persisted for as much as 30 minutes longer,” Treynor said.

Google did not disclose the full extent of the Gmail glitch but the brief outage was believed to have affected millions of people, including those using the service at work.

Complaints were posted online from Europe, Canada, United States and elsewhere.

An online Google Apps tracking dashboard, which indicated that a dozen services -- including Gmail and its social network Google+ -- had experienced problems.

"Whether the effect was brief or lasted the better part of an hour, please accept our apologies-we strive to make all of Google's services available and fast for you, all the time, and we missed the mark today," Treynor said.

"The issue has been resolved, and we're now focused on correcting the bug that caused the outage, as well as putting more checks and monitors in place to ensure that this kind of problem doesn't happen again,” Treynor added.

Gmail, which includes calendar and chat features, has soared in popularity over the past decade to become one of Google's most successful product offerings. With more than 420 million users, it has begun to make small inroads against Microsoft Exchange in the battle to provide email services for corporate customers as well as individual consumers.